1. Field
The present disclosure is generally related to medical or surgical microscopes, and particularly microscopes that allow for the movement of the objective lens during use.
2. Description of the Related Art
In the field of surgical microscopes it is well known to provide support structure for mounting the microscope and positioning the microscope in a comfortable position for the user and to obtain the best available viewing angle of the field of interest. The support structure typically includes multiple support arms that pivot about various axes to allow the microscope to be moved rather freely in three-dimensional space. There are many types of procedures to be observed with the microscope, such as dental procedures or surgeries, and ophthalmic surgery, as well as many other types of medical procedures that benefit from the high magnification provided by a surgical microscope.
It can be important for the user to have the eyepieces placed at a comfortable level and position so that the user can maintain the position over a long time period without causing undo fatigue. However, during a procedure it is often desirable to move the objective lens to a new position so that another field of interest can be viewed. Most prior art microscopes would require the entire microscope to be repositioned and the user would also likely be required to move to a new position. This repositioning of the microscope and the user disrupts and extends the time of surgery.
One prior art patent for a Surgical Microscope, U.S. Pat. No. 6,982,827, assigned to Carl-Zeiss-Stiftung, discloses a microscope where the objective lens can be moved about one axis without requiring the eyepieces to be moved. The movement of the objective lens without also moving the eyepieces is limited to only one axis. In addition, the tubular portion or rotation ring that allows the movement of the objective lens independent of the movement of the eyepieces, significantly limits the amount of objective lens movement available in the one axis before the viewed area of interest begins to be clipped-off (commonly referred to as vignetting) and significant aberrations begin to be introduced to the viewed image. Also, it is often desirable to move the objective lens in more than one axis of space.
Another prior art patent for an Operation Microscope, U.S. Pat. No. 4,448,498, assigned to Carl-Ziess-Stiftung, discloses a microscope using a pair of Risley Prisms (wedge prisms), to allow the field of view of the microscope to move about a circular area by the simultaneous rotation of two wedge prisms with respect to each other. FIG. 1 illustrates the movement of a focal point of a Risley Prism pair, such as is disclosed in U.S. Pat. No. 4,448,498. The lines 10 represent one center and two peripheral field points within the field of view of the wedge prisms 12 and 14. The center of circle 16 will follow the circumference of circle 18 and is controlled by rotation of prism 14 (reference number 20 and its associated arrows illustrates this relationship). The center of the field of view of the combined wedge prisms 12 and 14 follows the circumference of circle 16 and is controlled by rotation of prism 12 (reference number 22 and its associated arrows illustrates this relationship). The center of the field of view of the Risley prism pair 12 and 14 may be positioned at any point with the area of circle 24 and is controlled by the combined rotational positions of prisms 12 and 14. This combined rotation becomes quite complicated when moving from one position to a next position and requires two simultaneous and often opposite rotations of prisms 12 and 14.
An example of the required prism rotations follows. If a starting position in the center of circle 24 is at coordinates 0,0 and prisms 12 and 14 each deviate a light beam 10 degrees, the prisms 12 and 14 will be 180 degrees out of phase with each other. In other words, at coordinate 0,0 the thickest edge of prism 12 will be at 12 o'clock, and the thickest edge of prism 14 will be at 6 o'clock. Starting from the 0,0 position in order to move the field of view to a 10, 0 position (that is 10 units to the right along the x-axis), prism 12 needs to rotate approximately 13 degrees clockwise and prism 14 needs to rotate approximately 13 degrees counter-clockwise. This requires, in a manual system, for the operator to perform two separate rotations, in opposite directions. The operator would also need to somehow know and monitor the amount of rotation made and the amount of rotation required by the prisms 12 and 14. The first example above may appear straight forward because each prism rotates the same amount though in opposite directions. However, starting from position 0,10 (that is 10 units up along the y-axis), movement becomes more complex. To place the field of view of the prism pair 12 and 14 at coordinate 0,10 requires prism 12 to be rotated to approximately −77 degrees (relative to the starting position at 0,0) and prism 14 to be rotated to approximately −103 degrees. Then to move to position 10, 10 (10 units along the x-axis and 10 units along the y-axis) requires rotating prism 12 to a position of approximately −26 degrees and prism 14 to a position of approximately −64 degrees. Because of the required complicated rotations of Risley prisms 12 and 14, such rotations are typically controlled by motors, gears, and some type of controller with programming to control the amount and relative rotation of prisms 12 and 14, to move the field of view to a desired location within circle 24 based on input from a user interface, such as a joystick or control pad. Such automation adds significant cost to a microscope and the need for a surgeon to keep track of the user interface. In addition, to the complexity and cost of a Risley prism pair system, the Risley prisms can introduce additional glare and the resolution of the observed field is degraded compared to other objective lenses. Also, the amount of change in the focal point (size of circle 24) is limited by the wedge thickness of prisms 12 and 14.
Therefore, a need exists for a surgical microscope that allows the objective lens to be moved by a user easily and with no distraction in both pitch and roll directions of rotation, and without requiring the user to move. It is also desirable to provide an assembly that allows existing microscopes to be upgraded to provide the enhanced objective lens movement.